1. Field of the Invention
The present invention relates to a developer for developing electrostatic latent images in electrophotography, electrostatic recording and electrostatic printing. More specifically, the present invention is directed to a composition and method that provides a developer which comprises at least positively charged particles, negatively charged particles and a lubricant to ensure the elimination of ghosting and system contamination, as well as maintaining a stable, high quality image, during extended use.
2. Description of the Background
Visible image forming methods associated with toners using electro-photographic systems have been extensively studied and are currently widely used. Typical examples of these techniques are dual-component developing methods, which use image-forming particles and often larger carrier particles, and mono-component developing methods, which use a toner comprising only magnetic or non-magnetic image-forming particles. Details of such developing methods are described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., 9:261-275 (1994).
An image forming apparatus utilizing an electrophotographic method with toner is well known. In the image forming apparatus utilizing the electrophotographic method, images are generally formed onto a sheet of copy paper through the following processes.
After uniformly charging a photoconductor that serves as an image-holding body, images are exposed onto the surface of the charged photoconductor. Attenuating electrostatic charges during the exposure of light forms a latent image. Then the electrostatic latent images are visualized by developing with toner to form a toner image. The toner images are transferred onto the aforementioned medium and thereafter fixed on it by heating, pressure or solvent vapor.
In recent years, accompanying the rapid growth of computer technology, digital copiers and printers have been developed and become widely used. In these machines, monocomponent-developing methods have been applied more often to reduce the number of supply parts and ease of customer maintenance requirements compared with that of the dual component method.
In the mono-component systems, toner is generally required to have good fluidity and uniform chargeability in order to form a good quality visible image as described in U.S Pat. No. 5,802,284 incorporated herewithin by reference. The use of silica powder additives for toner particles to impart fluidity and chargeability properties has been widely studied and is one conventionally accepted method. Many US patents are known that include the use of silica or silicon dioxide with toner of various compositions. A subset of this prior art relates to surface treatments of silica or silicon dioxide for specific purposes to somehow enhance image quality characteristics relating to electrophotography. Examples of the use of hydrophobic silica particles for toner includes JP 46-5782 A, JP 48-47345A, and JP 48-47346A.
U.S. Pat. No. 5,464,722 and U.S. Pat. No. 5,447,815 disclose the manufacture of toners and the use of silicone oils and varnishes for treating toner additives, such as hydrophobic silica fine powder.
U.S. Pat. No. 4,868,084 includes the use of a silica treated with a silicone oil and alkyl silane or disilazane compound.
U.S. Pat. No. 5,702,858 and U.S. Pat. No. 5,561,019 are specific to the use of negatively charged hydrophobic silica treated with a silicone oil.
U.S. Pat. No. 4,902,570 discloses a process for treating metal oxides surfaces, such as silicon dioxide, by use of a modified ammonium-functional organopolysiloxane as a charge control substances for toners.
U.S. Pat. No. 4,618,556 discloses the use of a positive charge controller comprising fumed silica particles treated with a coupling agent bonded to either Si or Ti for use in a developer comprising a binder resin, colorant, and said positive charge controller.
U.S. Pat. No. 5,695,902 specifically describes the use of toner with an inorganic fine powder treated at least with silicone oil and a particular size composite metal oxide containing Si and Sr.
U.S. Pat. No. 6,004,711 discloses a toner composition with an extra-particulate additive having a negative charge and a second extra-particulate additive having a positive charge. This patent is concerned with addressing a problem of a wavy patterns formed when using a recoated or worn developer magnetic roller. The patent discloses that the toner composition therein includes conventional toner components in conventional amounts including zinc stearate, abrasives, microspheres, and the like.
Electrophotographic systems have also been known to include metal salts of fatty acids. For example, JP09-236942 discloses such metal salts to avoid the toner filming of an organic photoconductor (OPC) with the aid of cleaning blades. The metallic salt works to reduce this filming of the OPC drum and together with the use of spherical toner, filming has been shown to be greatly reduced. As the concentration of metallic fatty acid salts increase, the toner accepts charge more readily within a specified range. In this work, it was also found that if Ds50/Dt50 greater than 0.6, wherein Ds50 represents the volume median particle size of metallic salts of fatty acids and Dt50 represents the volume median particle size of the toner component particles, contamination of the laser printer machine components will occur resulting in prints with high background. If Ds84/Ds16 greater than 6, wherein Ds 84 represents the diameter at 84% of the accumulated undersize distribution curve of the metallic fatty acid particles and Ds16 represents the diameter at 16% of the accumulated undersize distribution curve of the metallic fatty acid particles, then the uniformity of the metallic salts of fatty acids particle size is broad and the charging stability exhibited in the toner is not acceptable. These particle size and particle size distribution values are as determined by a dry measurement technique using a Heros and Redos laser diffraction instrument manufactured by Sympatec.
In the actual toner composition product design, the silica particles must be carefully selected to minimize side effects such as environmental instability, ghosting, photo-conductor contamination, and photo-conductor charging system contamination as well as any adverse side-effects on image quality. Generally, silica particles have a finer particle size than toner particles and therefore the silica particles possess a larger specific surface area and higher charging properties which can largely influence overall toner performance.
Environmental stability improvement by modification of the silica surface with chemical treatment has been widely studied and reported. Hydrophobic treatment is an established method of providing environmental stability to the toner.
Ghosting is a typical defect often seen in monocomponent development systems and can be described as developed image forming toner patterns on a latent image-retaining member, which are electrostatically transferred to a transfer material such as paper and form either lighter images than the background or darker images than the background. In instances where the ghost image is lighter than the background, this phenomena is known as xe2x80x9cnegative ghostingxe2x80x9d and where the ghost image is darker than the background, this phenomenon is known as xe2x80x9cpositive ghosting.xe2x80x9d Because the ghosting phenomenon is complex and results from actual electrostatic printer orcopy machine system characteristics, toner flowability, toner triboelectric charge properties, and even exponential memory decay time of the photoconductor, the root cause is still not perfectly understood. It is often possible; however, to measure the distance between ghost images to determine which component makes the larger contribution to this undesirable imaging characteristic.
If the ghost image (negative or positive type) appears on the transfer material (paper) in proportion to the photoconductor circumference, this can usually be attributed to the photoconductive drum allowing a xe2x80x9cmemory defectxe2x80x9d to occur. I this case, the ghosting pattern normally repeats itself on the transferred media several times. If, however, the ghost image appears on the transfer paper in proportion to the development sleeve circumference, this can normally be associated with the periodically formed heterogeneous toner charge pattern on the development sleeve. In other words, if the charge properties of the toner are insufficiently balanced by adding the silica powder, ghosting, as described above, could occur. So, careful design of the addition of silica particles to the toner composition must be performed to avoid or minimize this ghosting. In addition to this, the design of the overall toner composition requires that there be minimal contamination by the toner to any of the electrophotographic system components, such as the photoconductor or (especially) the direct photoconductor charging apparatus.
Based on recent concerns regarding protection of the environment from ozone generating devices, an ozone-free (or greatly reduced) charging system is highly desirable and demanded by many customers. A conventional photo-conductor charging method such as the corotron and scorotron systems are simple in terms of manufacturing technique; however they also generate much ozone during operation. A contact photo-conductor charging method which generates much less ozone has been studied extensively and is now widely used. Generally, a charger in the system uses a solid conductive roller, referred to as the contact charging roller or CCR. The normally applied high voltage to the CCR generates a positive or negative charge with respect to the overall machine system. Oppositely charged substances may accumulate on the CCR and the photoconductor surface causing contamination and creating image defects such as spots or lines on the paper. These and other defects are attributable to remaining toner on the photo-conductor surface after the transfer step which can contaminate the CCR and the photoconductor by means of contact pressure between these two components. Another contributing factor is the electrostatic forces that exist between the toner and the CCR and the toner and the photoconductor.
It is thus desirable that the fine particles included to the overall toner composition be selected such that at least the requirement of elimination of ghosting, and the requirement that the CCR and photoconductor be less contaminated with undesirable accumulated toner, are ensured. Use of conventional toner compositions and techniques for use with specific printer and copy machines have been unsuccessful in improving performance and maintaining longevity of toner for these applications.
It is an object of the present invention to provide a toner-containing electrostatic developer composition, manufacture, and method of using such a composition wherein toner performance is controlled such that the toner is suitable for the specific development system, and is capable of a stable high image quality such as image density, background, resolution and other general requirements during long term use.
Another object of the present invention is to provide a toner that eliminates ghosting phenomena especially in monocomponent development systems.
Another object of the present invention is to provide a toner which is capable of stable long-term performance without any undesired toner contamination of the electrophotographic system including the photoconductor and direct photoconductor charging apparatus.
The objects of the present invention are obtainable by using an electrostatic developer which comprises a mixture of (1) toner components containing image-forming particles, (2) positively tribocharged particles, (3) negatively tribocharged particles, and (4) a lubricant.
The electrostatic developer components of the present invention comprises a mixture of (1) toner components containing image-forming particles, (2) positively tribocharged particles, (3) negatively tribocharged particles, and (4) a lubricant. Thus, the objects of the present invention are obtainable by using the above electrostatic developer.
The objects of the present invention are more preferably obtainable when the lubricant is a specified metallic fatty acid salt particle with the following chemical structure:
M{OOCxe2x80x94(CH2)nxe2x80x94CH3}m
where n=5-100, m=1-5 and M denotes mono or multivalent cation(s).
The objects of the present invention are even more preferably obtainable when the lubricant is the above-specified metallic fatty acid salt particle wherein the ratio of Ds50/Dt50xe2x89xa60.9, and even more preferably xe2x89xa60.6, where Ds50 is the median volume diameter of the metallic fatty acid particles and Dt50 is the median volume diameter of the toner particles, and/or wherein the ratio of Ds84/Ds16xe2x89xa78.0, where Ds84 represents the diameter at 84% of the accumulated undersize distribution curve of the metal fatty acid salt particles and Ds16 represents the diameter at 16% of the accumulated undersize distribution curve of the fatty metal acid particles, respectively.
The above combination of components allows for high image density and clear images without ghost images or background formed during the electrophotography process. The development of this process is at high-resolution power and indicates improved electrostatic recording is obtainable.
In electrophotography, electrostatic recording, or the like, in which the developing method and the toner according to the present invention are used, the image-forming particles do not transfer to the non-image area and clear images can be formed, as well as unnecessary consumption of the image-forming particles can be suppressed, thereby providing great industrial merit. The invention provides for elimination of the phenomenon described as ghosting and background and results in better long-life results.
Toner Components
The toner in the present invention can be prepared by any of the generally known methods in the art and various known toner constituent ingredients can be used. In addition, the possibility exists to utilize xe2x80x9cpolymerizedxe2x80x9d toner.
For xe2x80x9cnon-polymerizedxe2x80x9d or conventional toner, the binder resin for the toner can be selected from a wide variety of materials including known thermoplastic resins. There can be mentioned, for example, styrene resin (homo- or copolymer containing styrene or substituted styrene) such as a polystyrene, polychlorostyrene, poly- -methylstyrene, styrene-chlorostyrene polymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylate copolymer (for example, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylate copolymer (for example, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer and styrene-phenyl methacrylate copolymer), styrene-methyl xc3xa1-chloroacrylate copolymer and styrene-acrylonitrile-acrylate copolymer, vinyl chloride resin, resin modified maleic acid resin, phenolic resin, epoxy resin, saturated or unsaturated polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin and polyvinyl butyral resin. Preferred resins include styrene resin, and saturated or unsaturated polyester resin. Further, the above-mentioned resins may be used not only alone, but also as a combination of two or more of them.
In order to use the toner of the present invention in the form of a magnetic toner, magnetic powder generally known in the art may also be incorporated therein. The magnetic powder for the toner of the present invention is preferably chosen from the ferromagnetic materials exhibiting ferromagnetism including ferrimagnetism in a working circumstance temperature (around 0xc2x0 to 60xc2x0 C.) for office business machines, plain paper copiers, printers, etc. For example, there can be mentioned magnetic powder showing ferromagnetism or ferrimagnetism in a temperature range of about 0xc2x0 to 60xc2x0 C., selected from magnetite (Fe3O4), maghemite (xe2x80x94Fe2O3), a complex of magnetite and maghemite, spinal ferrite such as ferrite (MxFe3xe2x88x92xO4 in which M represents Mn, Fe, Co, Ni, Cu, Mg, Zn, Cd or mixed crystal materials thereof), hexagonal ferrites such as BaO.6Fe2O3, garnet-type oxide such as Y3 Fe5O12, retile-type oxide such as CrO2, metal such as Fe, Mn, Ni, Co, and Cr, as well as other ferromagnetic alloys. Among them, a powder of magnetite, maghemite or a complex product of magnetite and maghemite with an average particle size of not more the 3 xcexcm, more preferably about 0.01 to 1 xcexcm are preferred in view of the performance and the cost. The above-mentioned magnetic powder may be used not only alone but also as a combination of two or more of them.
As an example of manufacture of a mono-component electrostatic developer containing a magnetic toner, the blending weight ratio of the binder resin to the magnetic powder can be selected within a range from 1:3 to 7:1, while taking the fixing property to a transfer material into consideration.
As a colorant used for the toner, any of known dyes and pigments such as carbon black, lamp black, ultramarine, nigrosine dye, aniline blue, phthalocyanine blue, phthalocyanine green, hanza yellow G, rhodamine type dye and pigment, chrome yellow, quinacridone, benzidine yellow, rose bengale, triallylmethane dyes, monoazo and disazo dyes and pigments may be used alone or in admixture. The addition amount of the colorant into the toner is preferably from 0.1 to 30 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the binder resin. The fixing properties become poor if the amount is excessive, thus showing tendencies in property performance that is undesirable.
The toner used in the present invention may preferably contain a low-molecular weight wax in an amount of from 0.1 parts to 20 parts by weight, and more preferably from 0.5 to 10 parts by weight, based on 100 parts by weight of the binder resin component. The low-molecular weight wax contained in the magnetic toner of the present invention may include the following: alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin and paraffin wax, aliphatic hydrocarbon waxes such as low-molecular weight polypropylene, hydrocarbon waxes, such as oxidized polyethylene wax; block copolymers of these; waxes mainly composed of aliphatic esters, such as carnauba wax, saozole wax and monotate wax; and waxes obtained by deodorizing partly or wholly fatty acid esters, such as deodorized carnauba wax. It may also include straight chain saturated fatty acids such as palmitic acid, stearic acid and montanic acid; unsaturated fatty acids such as brassidic acid, eleostearic acid and parinnaric acid; saturated alcohols such as stearyl alcohol aralkyl alcohol, behenyl alcohol, carnaubyl alcohol, cetyl alcohol and melissyl alcohol; polyhydric alcohols such as sorbitol; fatty acid amides such as linolic acid amide, oleic acid amide, and lauric acid amide; saturated fatty acid bisamides such as methylenebisstearic acid amide, ethylenebiscapric acid amide, ethylenebislauric acid amide, and hexamethylenebisstearic acid amide; unsaturated fatty amides such as ethylenebisoleic acid amide, hexamethylenebisoleic acid amide, N,Nxe2x80x2-bisdi-oleyladipic acid amide and N,Nxe2x80x2-bisdioleylsebacic acid amide; aromatic bisamides such as xylenebisstearic acid amide and N,Nxe2x80x2-distearylisophthalic acid amide; fatty acid metal: salts (what are commonly called metal soaps) such as calcium stearate, calcium laurate, zinc stearate, and magnesium stearate; waxes obtained by grafting vinyl monomers such as styrene and acrylic acid onto aliphatic hydrocarbon waxes; partially esterified products of fatty acids such as behenic acid monoglyceride with polyhydric alcohols; and methyl ester compounds having a hydroxyl group, obtained by hydrogenation of vegetable fats and oils.
In addition, auxiliary agents such as various kinds of plasticizers and releasing agents may also be added to the toner for adjusting thermal properties, physical properties, etc. The addition amount thereof is preferably from 0.1 to 10 parts by weight based on 100 parts by weight of the toner.
The charging property of the toner in the present invention may be controlled by the binder resin or the dye and pigment per se and, if required, a charge control agent causing no problem in view of the color reproduction may also be used together. It is also possible to include charge control resins.
Examples of the charge controller are well known by way of reference for example, U.S. Pat. No. 4,957,840. For positive charge control agents, examples may include: nigrosine and its modification products modified by a fatty acid metal salt; quaternary ammonium salts such as tributylbenzyl-ammonium-1 hydroxy-4-naphthosulfonic acid salt, and tetrabutylammonium tetrafluoroborate; diorganotin oxides, such as dibutyltin oxide, dioctyltin oxide, and dicyclohexyltin oxide; and diorganotin borates, such as dibutyltin borate, dioctyltin borate, and dicyclo-hexyltin borate; and triphenylmethane compound. These positive charge controllers maybe used singularly or as a mixture of two or more species. As another type of positive charge controller, there may be use of a homopolymer of a monomer having an amino group represented by the formula: 
wherein R1 represents H or CH3; and R2 and R3 each represent a substituted or unsubstituted alkyl group (preferably C1-C4); or a copolymer of the monomer having an amine group with another polymerizable monomer such as styrene, acrylates, and methacrylates as described above. In this case, the positive charge controller may also play functions as a binder.
Examples of negative charge control agents include: metal complexes or salts of monoazo dyes, salicylic acid, alkylsalicylic acid, dialkylsalicylic acid, naphthonic acid, or acetylacetone. It is preferred that the above-mentioned charge controller is used in the form of fine powder. In such a case, the number-average particle size thereof may preferably be 4 microns or smaller, more preferably 3 microns or smaller.
In the case of internal addition, such charge controller may preferably be used in an amount of 0.1-20 wt. parts, more preferably 0.2-10 wt. parts, per 100 wt. parts of a binder resin by taking into consideration the conditions for the manufacturing method including the chargeability of the binder resin, the addition amount of the colorant and the dispersion method, as well as the chargeability of the other additives.
The toner in the present invention may preferably have a volume median particle size from 4 to 20 xcexcm, more preferably from 5 to 15 xcexcm, and most preferably from 6 to 12 xcexcm, where the volume median particle size is obtained by using a Coulter counter Model Multisizer with a 100 micron aperture.
Positively Charged Particles and Negatively Charged Particles
The negatively tribocharged particles and positively tribocharged particles used in the present invention are hydrophobic and maybe prepared by any of the methods known in the art. These particles also can be prepared by the proper treatment of organic particles and/or inorganic particles.
The organic particles that are employed in the toner compositions may be preferably chosen from resinous materials. Examples of such resinous materials are exemplified by, but not limited to, thermoplastic resins such as polystyrenes, polymethyl methacrylate, polyolefin resins, polyamide resins, polycarbonate resins, polyether resins, polysulfone resins, polyester resins, epoxy resins, polybutyral resins, urea resins, urethane/urea resins, silicon resins, polyethytlene resins, Teflon resins and the like (fluoropolymer resins), thermosetting resins, a mixture thereof, block copolymers thereof, graft copolymers thereof, a blend thereof, and the like.
The inorganic oxide particles that are employed for toner compositions may also be prepared by any methods known in the art and are preferably selected from the group consisting of SiO2, Al2O3, W2O3, ZrO2, SeO, TiO2, ZnO and MgO. The particles preferably have a BET measurement value of not less than 1 m2/g, more preferably not less than 30 m2/g and even more preferably not less than 100 m2/g.
In a preferred embodiment, the negatively charged particles comprise a chemically treated fumed silica which is prepared by gaseous phase oxidation of a silicon compound or colloidal silica which is prepared by a liquid phase chemical reaction. A material which can be preferably used for chemical treatment is an organic silicon compound and examples include, but are not limited to, organodisilazane such as hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethyoxysilane, dimethyldichlorosilane, methyltriclorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptans, triorganosilylacrylates, vinyldimethylacetoxysilane, diorganomethoxysilanes, cyclic organosiloxanes such as dimethyl cyclopolysiloxane, e.g., octamethyl cyclotetrasiloxane (OCTS), 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyl-disiloxane, fluorinated siloxane, polymethylphenylsiloxane, dimethylpolysiloxane, and polydimethylsiloxane. Silica particles may be treated with one or more organic silicon compounds to render a negative charge property as well as hydrophobic characteristics. Examples of such treatment are as described in U.S. Pat. No. 5,686,054, which is hereby incorporated by reference, where the organosilicon compounds employed are preferably organosilanes of the formula:
R1nSiX4xe2x88x92n
in which R1 is identical or different and is monovalent, optionally halogenated, hydrocarbon radical having 1 to 18 carbon atoms,
X is identical or different and is a halogen, preferably chlorine, or OH, OR2, OCOR2, O(CH2)xOR2,
R2 is identical or different and is monovalent hydrocarbon radical having 1 to 8 carbon atoms,
n is 1 or 2, preferably 2, and
x is 1,2 or 3 preferably 1, and/or
organosiloxanes of the formula
(R1aXbSiO1/2)z(R12SiO2/2)x(R3R1SiO2/2)y(SiXbR1a)z in which
R1 is as defined above
R2 is as defined above,
R3 is identical or different, is a hydrogen or a monovalent, optionally halogenated, hydrocarbon radical having 1 to 18 carbon atoms which is different from R1,
X is as defined above, preferably OH,
a is 0, 1, 2, or 3, preferably 2,
b is 0, 1, 2, or 3, preferably 1, the sum of A+B being equal to 3,
x is 0 or an integer from 1 to 200, preferably from 10 to 50,
y is 0 or an integer from 1 to 200, with x to y preferably being at least equal to 5 to 1, and the sum x+y being equal to 0 or an integer between 1 and 200, preferably from 10 to 50,
z is 0 or 1 with the proviso that z is greater than 0 if the sum of x+y is 0, and z is preferably 1.
The positively charged particles used in the present invention can be prepared by any known method in art. In a preferred embodiment, the positively charged particles comprise chemically treated fumed silica or colloidal silica. Preferable material which can be used for the chemical treatment includes a silicon compound having a nitrogen atom combined in the structure. Examples include, but are not limited to, amninopropyltrimethoxysilane, aminopropyltriethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, monobutylaminopropyldimethylmethoxysilane, dibutylamninopropyldiethylmonomethoxysilane, dimethylaminophenylethoxysilane, gamma-propylphenylamine, substituted trimethoxysilane, and gamma-propylmorpholine-substituted trimethoxysilane.
A process of manufacturing modified silica is described in Barthel et al, xe2x80x9cThe Surface Modification of Silicas on the Free Flow and Charging Properties of Monocomponent Magnetic Toners,xe2x80x9d included the 1996 edition of the International Conference on Digital Printing Technologies, NIP 12, sponsored by the Imaging Sciences and Technology Society, pp. 511-516.
The negatively charged particles and positively charged particles which are composed of organic or inorganic oxide particles subjected to any of the aforementioned treatments may be used in any amount, and preferably in a ghost-reducing effective amount. This amount is more preferably within a range of about 0.01 to 5 parts, and even more preferably 0.5 to 3 parts, by weight based on 100 parts by weight of the image-forming particles.
Lubricant
The toner used in the present invention contains a lubricant, preferably selected from the group of metallic fatty acid salts with the following chemical structure:
M{OOCxe2x80x94(CH2)nxe2x80x94CH3}m
where n=5-100, m=1-5 and M denotes mono or multivalent cation(s) including; Li, Na, Mg, Al, Zn, K, Ca, Cu, Co, Cr, Fe, Ni, Be, Rb, Ag, Sr, and Ba, and more preferably said metal fatty acid salt particle with a Ds50/Dt50xe2x89xa60.9, and even more preferably with a Ds50/Dt50xe2x89xa60.6, where_Ds50 is the median volume diameter of the metal fatty acid particle grain size and Dt50 is the median volume diameter of the toner particle grain size and/or Ds84/Ds16xe2x89xa68.0, where Ds84 represents the diameter at 84% of the accumulated undersize distribution curve of the metal salt of the metallic fatty acid particle grain size and Ds16 represents the diameter at 16% of the accumulated undersize distribution curve of the metal salt of the metallic fatty acid particle grain size, respectively. The metallic salt of a fatty acid is preferably comprised within a range where n=6-18, and where the preferred metal is often Zinc.
Counter ions of the metallic fatty acid salt that can be used include Li, Na, K, Cu, Rb, Ag, Zn, Mg, Ca, Sr, Al, Fe, Co, and Ni. Best results were obtained using Zn, Mg, Ca, and Al stearates.
Lubricants have been successfully used that are based on a combination of Zn stearate, palmitate, and myristate, or Zn stearate with minor amounts, such as up to 3% of the unreacted stearic acid and other insignificant impurites. The most preferred lubricant is a mixture of 56% zinc stearate, 40% zinc palmitate and 2% zinc myristate with a median particle size of 2-5 microns.
The lubricant is present in accumulated toner contamination-reducing effective amounts, i.e., amounts sufficient to avoid or at least reduce contamination of the CCR and photoconductor, and image defects, by undesirable accumulated toner after multiple printings, and thus in amounts sufficient to extend the useful life of the CCR and photoconductor before cleaning or replacement. The amount of lubricant is generally within a range of about 0.01-5.0 parts, and even more preferably 0.01-2.0 parts, by weight based on 100 parts by weight of the image-forming particles.
The present invention also includes a method of reducing or eliminating contamination of a photoconductive drum assembly or a direct pliotoconductor charging apparatus or both, which comprises carrying out electrostatic development in the presence of same with the electrostatic developer composition of the present invention, and wherein the photoconductive drum assembly can be an organic photoconductor and the photoconductor charging apparatus can be a contact charge roller.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. These examples describe, but are not limited to, the preparation of toner by conventional process means as described below.